Surface Review and Letters

Recent studies (I. G. Shuttleworth, Surf. Rev. Lett.14(2) (2007) 321) have demonstrated a direct method of diffraction pattern inversion for the helium atom scattering (HAS) experiment. The method requires the expansion of the Patterson function as a multivariate Taylor series to form a set of simultaneous equations. Benchmark tests of the procedure show that incomplete Taylor expansions introduce inconsistency into the set of simultaneous equations, whereas larger Taylor expansions attract significant numerical errors during their solution. The current work replaces the conventional matrix inversion techniques with a multidimensional Newton–Raphson algorithm. Tests have shown that the Newton–Raphson procedure removes the Taylor series and numerical limitations from the inversion technique for any realistic surface.

The formation mechanism and surface evolution of thin silver films deposited on silicone oil substrates by a DC-magnetron sputtering method are reported. As the film thickness increases, the deposited silver atoms first form compact clusters, then transfer to ramified aggregates and finally form a continuous film on the liquid substrate. After deposition, the surface morphology of the silver film is susceptible to evolve successively in the atmosphere condition, resulting in the formation of broad cracks and straight-sided (or worm-like) wrinkles. The evolution behaviors and underlying physical mechanisms of the cracks and wrinkles are presented and discussed in detail.

4-Amino-decylpyridinium bromide (ADPBr), an antimicrobial surface active agent, was synthesized by quaternization of 4-aminopyridine (AP) with decyl bromide (DBr). The reaction was carried out at 1:1.2 molar ratio of reactants (4-aminopyridine and decyl bromide, respectively) at 200°C for 10 min. The maximum yield of the product was 74.6%. The structure of the synthesized product was characterized by using modern analytical techniques, such as FT-IR, ¹H NMR, and ¹³C NMR. The antimicrobial activity of the salt was evaluated with minimum inhibition concentration method and showed good activity against gram-negative bacteria. The MIC of the salt was found to be 600 ppm for 2 × 10⁴ CFU/mL of E. coli.

Matrine is an important natural occurring component in sophora roots. It has a wide range of pharmacological actions. In this work, electrochemical investigation of matrine and its interaction with L-cysteine (L-Cys) is reported. Via the electrochemical approach, we have proved that the distribution coefficients of protonated and deprotonated matrine affect its electrochemical response on Au or L-Cys modified Au electrodes. The study by ultraviolet spectroscopy also finds that the molecular interaction between matrine and L-Cys changes with the distribution coefficients of protonated and deprotonated matrine at different pH value. Compared with the response of matrine on the bare gold electrode, the L-Cys/Au self-assembled monolayers modified electrodes exhibit obviously higher current response toward matrine oxidation. The oxidation current of matrine at L-Cys assembled electrode has a good linear relation in the range of 0.2–5 mM, with the correlation coefficient of 0.989 by cyclic voltammagrams. Electrochemical combined with spectroscopic techniques would provide relatively easy way to better understand the underlying mechanism of matrine/L-Cys interaction and will be helpful for the development of electroanalytical techniques for the determination of matrine.

α-Fe₂O₃@ATO (antimony doped tin oxide) nanocomposite particles with core–shell structure were prepared by homogeneous precipitation method using monodispersed α-Fe₂O₃ (hematite) nanoparticles as cores, SnCl₄ · 5H₂O and SbCl₃ as the precursor of the shell. The morphology and structure of the nanocomposite particles were studied with transmission electron microscopy and X-ray diffraction, respectively. The electricity properties of the nanocomposite were also investigated in terms of coating amount, molar ratio of element Sb to Sn, and heat treatment conditions. The results showed that the conditions of ATO/α-Fe₂O₃ (weight ratio) = 70%, n(Sb)/n(Sn) = 10%, calcined at 700°C for 1 h were optimal for the conductivity of the nanocomposite.

Highly (002)-oriented nanocrystalline ZnO thin films were deposited on glass substrates at a substrate temperature of 500°C in air atmosphere by low-cost spray pyrolysis method. Room temperature photoluminescence spectral studies show the presence of near band edge emission and defect level emission (DLE) from the samples. The DLE wavelength is blueshifted about 22 nm and further emission intensity enhancement is observed in (002)-oriented sample as compared to that of wurtzite ZnO phase. The modifications in local defect levels and change in crystalline symmetry are attributed to the blue shift in the DLE region of c-axis oriented sample. The increased emission intensity of (002)-oriented samples is due to improvement in crystalline quality, preferential oriented growth and spherical morphology of nanocrystalline grains.

Field-ion microscopy and molecular dynamics simulation were used for the characterization of the translation states at special grain boundaries in tungsten. It is revealed that rigid-body displacement had the component of displacement parallel to the [110] direction equal to 0 or 1 interplanar spacing. Full vectors of lateral shifts are described by broad statistical distribution. The mathematical simulation revealed two mirror-symmetry-breaking lateral translations along the direction of the Σ9 grain boundary corresponding to different atomic structures. It is shown that the partial disconnection with the Burgers vector can be considered as the elemental carriers of grain-boundary polymorphic transformation.

Based on the Density Functional Theory (DFT) with noncollinear-magnetism formulations, we have calculated the magnetism of single 3d transition-metal atoms and the magnetic anisotropies of supported Ni chains on the Au(110)-(1 × 2) surface. Our results for single absorbed 3d transition-metal atoms show that the surface relaxations enhance the orbital moments of left-end elements (Ti, V) and quenches the orbital moments of right-end elements (Fe, Co, Ni) on the Au(110)-(1 × 2) surface. The magnetic anisotropies of Ni atomic chains on the surface are closely related to orbital quenching. The easy magnetized axes change from the direction parallel to the chains to the direction perpendicular to the Ni chains when they absorb on the surface.

Silicon nitride (Si₃N₄) has attracted substantial interest because of its extreme chemical and physical properties, but the sintering densification of Si₃N₄ is difficult, and it is easily oxidized in the high-temperature air to impact high-temperature strength, which restricts its applied range. In order to decrease the oxidization and improve the strength of Si₃N₄ at high temperature, the surface of Si₃N₄ is coated with Al(OH)₃ and Y(OH)₃ to synthesis Si₃N₄@Al(OH)₃–Y(OH)₃ core-shell composite particles. Through TEM, XRD, and BET analysis, when pH is about 9, Si₃N₄@Al(OH)₃–Y(OH)₃ core-shell composite particles are successfully synthesized by co-precipitation methods. Coating layer is about 200 nm, which is compaction and conformability. Dispersion of coated Si₃N₄ with Al(OH)₃ and Y(OH)₃ particles are very good. Synthesis of Si₃N₄@Al(OH)₃–Y(OH)₃ core-shell composite powder will lay the foundation for preparing high-performance YAG/Si₃N₄ multiphase ceramic materials.

The effects of plating temperature on the plating rate, P content, surface morphology, and electrical resistance of the electroless Ni–P deposits were studied. The results showed that the deposition rate of the Ni–P deposit and P content of the Ni–P layer increased with the rise of temperature of the plating bath. Scanning electron microscopy of the Ni–P deposits showed a nodule structure. The Ni–P plating layers had an amorphous structure and surface resistance of the layer decreased with the rise of temperature. In addition, the electromagnetic interference shielding effectiveness (EMI SE) of electroless Ni–P plated polyester fabric was also investigated. The result indicated that EMI SE of Ni–P plated polyester fabric was close to 45–50 dB when the surface resistance was 0.63 Ω/□.

Sample preparation is an important procedure for atomic force microscope (AFM) studies. However, flexible virus particles have a tendency to aggregate together and are easily compressed during sample preparation or by AFM tip that subsequently hamper studying of virus by AFM. Herein, low concentration chemical reagent of glutaraldehyde (2%, v/v) is pre-mixed in virus suspension that facilitates the dispersion and observation of recombinant serotype 2 adeno-associated virus particles deposited on mica surface with little deformation.

The effective elastic modulus and fracture toughness of the nanofilm were derived with the surface relaxation and the surface energy taken into consideration by means of the interatomic potential of an ideal crystal. The size effects of the effective elastic modulus and fracture toughness were discussed when the thickness of the nanofilm was reduced. And the dependence of the size effects on the surface relaxation and surface energy was also analyzed.

In the conventional Avrami–Kolmogorov–Johnson–Mehl model, the reaction or phase transition occurring in the 2D or 3D infinite medium is considered to start and proceed around randomly distributed and/or appearing nucleation centers. The radius of the regions transformed is assumed to linearly increase with time. The Monte Carlo simulations presented, illustrate what may happen if the transformation takes place in nanoparticles. The attention is focused on nucleation on the regular surface, edge and corner sites, and on the dependence of the activation energy for elementary reaction events on the local state of the sites.

The Flicker Noise Analysis methodology is applied on voltage signals recorded when the electrochemical etching of crystalline surfaces of silicon is performed. The porous silicon material resulting from this procedure is composed of nanocrystals possessing remarkable properties which can be employed in the development of optical, electronic, or biological sensor devices. As a result of the analysis, two dynamic processes during the electrochemical reaction have been identified: one related to the dissolution of the crystalline matrix and the other related to the porous morphology itself.

The magnetic properties and giant magnetostriction effect (GMS) of the amorphous alternant [Tb/Fe/Dy]_n (named S1) and [Fe/Tb/Fe/Dy]_m (named S2) nano-multilayer films have been studied. The magnetic hysteresis loops show that easy magnetic direction changes from perpendicular to the film plane (S1) to parallel to the film plane (S2). S2 has better soft magnetic properties and low-field giant magnetostriction effect than that of S1, due to the exchanging interaction between the hard GMS layer and the soft layer Fe. The different magnetic behavior is explained by considering the nature of the magnetization process, i.e. domain-wall motion and spin rotation.

This work aims to investigate the effect of two different counterdisc materials, i.e. gray cast iron (GCI) and ductile gray cast iron (DGCI) on tribo behavior of non-commercial frictional materials (NF1, NF2, NF4, and NF5) and two other chosen commercial brake pads (CMA and CMB) under dry sliding contact conditions. The four non-commercial frictional materials were fabricated with various percentages of phenolic binder resin (15 and 20 vol.%) and reinforced with steel fibers (15 and 20 vol.%) using hot press molding methods. Tribo tests were carried out using a small-scale tribo-tester of pad-on-disc type. Friction coefficient and wear of non-commercial and commercial brake pads were measured against each counterdisc (GCI and DGCI) and compared. Then, the friction and wear characteristic are discussed by comparing the experimental results obtained for each kind of cast iron.

The results showed that maximum friction coefficient (0.4–0.5) of brake pad was attained at 2.22 MPa applied pressure and 2.1 m/s sliding speed when the frictional brake pad materials were tested against DGCI disc rotor. Meanwhile, similar wear rates for all frictional brake pad materials were sustained at higher applied pressure and sliding speed when tested against either type of rotor discs (GCI and DGCI).

The results on the other hand, indicated that non-commercial materials NF1 and NF4, gave better wear resistance compared to other frictional pad materials. NF2 exhibited the lowest wear resistance when tested against GCI and DGCI rotor disc at all applied pressure and sliding speeds. The latter result is referred to the low percentage binder resin in the friction material NF2.

Surface and bulk plasmon excitations from the ordering Pt₈₀Co₂₀(111) alloy surface are studied by means electron energy loss spectroscopy in the low energy range of the primary electron energy E₀. Deviation of the plasmon excitations from the theoretical value was found for Pt, Co metals, and Pt₈₀Co₂₀(111) alloy as calculated in the free-electron gas model. For the ordered alloy, the bulk plasmon energy is 2–3 eV more than for the disordered alloy, whereas the difference for surface plasmon energy is 4–7 eV in the range E₀ = 150–800 eV. The ration of intensity lines of plasmons η from E₀ was investigated for the (dis)ordered state of the Pt₈₀Co₂₀(111) alloy surface. For the ordered alloy, η has prolonged dependence from energy E₀ in comparison with the disordered alloy. The relationship between layer-by-layer surface concentration and surface plasmon damping was observed.

In order to improve the high-temperature behaviors of hot work die steel in engineering application, the high-temperature wear and thermal fatigue behavior of brush plating Ni/nano-SiO₂ composite coating have been investigated. The microstructure of Ni/nano-SiO₂ composite coating has been analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). TEM observation of Ni/nano-SiO₂ composite coating has shown that the added SiO₂ particle with an average size of about 20 nm is uniformly distributed in Nickel matrix. The high-temperature wear behavior of Ni/nano-SiO₂ composite coating has been investigated using a ball-on–block test rig. The results from the high-temperature wear behaviors studies indicate that the steady-state friction coefficient and the specific wear rate of Ni/nano-SiO₂ composite coating are lower than that of Cr12MoNi steel. The thermal fatigue tests were fulfilled by heating and quenching in water at a cycle period of 2 min. The results of thermal fatigue testing show that brush plating Ni/nano-SiO₂ composite coating can improve thermal fatigue resistance as compared to the Cr12MoNi hot rolling tool steel.

Cathodic arc physical vapor deposition (CAPVD) a technique used for the deposition of hard coatings for tooling applications has many advantages. The main drawback of this technique is the formation of macrodroplets (MDs) during deposition resulting in films with rougher morphology. The MDs contamination and growth mechanisms was investigated in TiN coatings over high-speed steel, as a function of metal ion etching, substrate bias, and nitrogen gas flow rate; it was observed that the latter is the most important factor in controlling the size and number of the macrodroplets.

The adsorption of Ni atom on the Mo(110) surface has been studied within the density functional theory framework. It turned out that Ni–Mo surface alloy was formed with Ni atoms substituting Mo atom in the outermost layer. The subsurface site adsorption was found to be not preferred. Geometric analysis showed that the rumpling between substitutional Ni and Mo in the first alloy layer was about 0.108 Å at medium and low coverage (Θ). In addition, the diffusion of Ni on bare and Ni-substitutional Mo(110) surface has been investigated. It was shown that the diffusion energy barrier was reduced as the increase of coverage on bare Mo(110) surface, which supports the switch of growth mode layer-by-layer to Stranski–Krastanov as the function of coverage. Substitutional Ni atom only slightly increases the energy barrier for Ni diffusion on Mo(110) surface.

Salt bath oxinitriding is a duplex surface treatment developed to improve tribological and corrosion properties of ferrous materials. In this research, gray cast iron samples were nitrided at the temperature range of 480°C–580°C, and then oxidized in an oxidative salt bath. The phase composition of surface layer was identified by X-ray diffraction. Using a microhardness tester, hardness of nitrided gray cast iron was measured. Corrosion behavior of treated (nitrided and oxinitrided) samples was evaluated using potentiodynamic polarization technique in 3.5% NaCl solution. XRD analyses indicate that the surface layer in nitrided and oxinitrided samples is composed of ε-iron nitride (Fe_2-3N) and magnetite (Fe₃O₄), respectively. Results show that the corrosion resistance of gray cast iron can be improved up to 170%.

Surface oxidation of Ti was carried out using KrF excimer laser in the presence of O₂. Different colors were obtained by varying the number of laser pulses at the fixed laser fluence. X-ray photoelectron spectroscopy shows that the outmost surface is composed of TiO₂ and the inner layer consists of TiO and Ti₂O₃ as well as TiO₂. Fractions of titanium chemical states stabilized at 33% TiO, 63% TiO₂, and 2% Ti₂O₃ with increasing number of laser pulses. The surface roughness tends to increase with number of laser pulses. It is suggested that compositional variation and morphological difference contribute to the laser-induced surface coloration.

Bayerite sol is spun onto single crystal Si substrate, after synthesis and optimization, to obtain films of thickness ~ 0.2 μm. The deposited films are room temperature dried and then heated up to a temperature of 350°C in order to obtain Al₂O₃. Surface and structural changes, during heating, are observed with optical microscopy. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) are used for post-treatment analyses/characterization. The as-deposited and heated samples' surfaces are smooth as seen with optical and scanning electron microscope in case of optimized conditions. XRD patterns show the change from amorphous to crystalline behavior of these films when heated under various conditions. The most stable form of aluminum oxide, i.e. α-Al₂O₃, is obtained when samples are heated up to a temperature of as low as 350°C. The thin films are also deposited onto sodalime glass substrates in order to confirm Al₂O₃ formation through band gap probing. Photoconduction is used to find the energy band gap, which comes out to be 4.7 eV; lower value is correlated to the defect induced states in the band gap.

Cluster-like network structures of single-walled carbon nanotubes (SWNTs) were synthesized by chemical grafting poly 2-hydroxyethyl methacrylate (polyHEMA) to the sidewalls of SWNTs. Acid chloride-functionalized tubes were coupled with commercially available HEMA monomer, which was in turn polymerized using a radical initiator. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to identify the surface changes on the nanocomposites. Microscopic observations of the nanotube complexes by field emission scanning electron microscopy (FE-SEM) show that the tubes were dispersed and formed cluster-like network, branched structures with less bundling, thus, strongly suggesting a firm coating of the polymer on nanotube walls. The coating was further confirmed by transmission electron microscopy. The thermal properties of the nanotube complex as studied by thermal gravimetric analysis (TGA) revealed that coating enhanced stability of the complex, when compared to that of bulk polyHEMA and pristine SWNTs. The nanotube complexes showed excellent suspension stability when dispersed in organic solvent.

PN photodiodes, as an alternative form of photodetectors, is based on carrier production in the high-field junction region, and it has a response time considerably faster than that of a photoconductor and is typically in the order of nanoseconds. Photodetectors operating in the short wavelength ultraviolet (UV) region are important devices that can be used in various commercial and military applications. In the present work, we fabricated the p-GaN/n-Si heterojunction photodiode to observe the photoelectric effects. From the results, the current–voltage characteristics of the device show the typical rectifying behavior of heterojunctions. The UV photocurrent measurement was performed using an Hg-lamp under a reverse bias.

Poly(phthalazinone ether nitrile) (PPEN) block copolymers containing polysiloxane were prepared so as to create a strongly hydrophobic polymer surface. The copolymers were synthesized from eugenol end-capped polydimethylsiloxane (PDMS) and fluoro-terminated PPEN oligomers by the aromatic nucleophilic substitution polycondensation in the presence of dimethyl sulfoxide/o-dichlorobenzene and K₂CO₃ as solvents and catalyst, respectively. The resultant copolymers were characterized by FTIR, ¹H NMR, and gel permeation chromatography. XPS analysis results indicated that the copolymer film had a very rich PDMS segment surface. Atomic force microscopy further showed that there existed a continuous PDMS phase on the copolymer surface and PPEN as the dispersive particles was dispersed at diameters between 0.1 and 0.3 nm. The enrichment of PDMS in the copolymer surface could be responsible for an increase of surface water repellency (113.4°).